Vet View: Fighting Fluke

by Dr Vicki Henderson, Clyde Vet Group

Farmers across Scotland will be well aware of the risks that liver fluke (Fasciola hepatica) poses to their stock, and most will treat their cattle and sheep with some form of flukicide at some point during the year.   

Whilst routine treatment for fluke is part of the farming calendar in Scotland, there are a few tools that can help make sure these steps are timely and appropriate to get the most benefit. 

Fluke forecasting 

As the life cycle of the fluke is highly dependant on climate, forecasts have been developed by NADIS that help to predict the risk of fluke based on the local weather conditions each year. Knowledge of when the infectious larvae levels are high on pasture will help to target autumn/early winter dosing so that immature fluke are treated at the right time.  

Fluke testing 

There are several ways to test for fluke and they all have different merits and demerits.  

All dung sampling is best taken from at least 10 separate animals and not pooled before it is handed over to the vets.  

Faecal sedimentation is a quick, reliable test to look for fluke eggs in dung that can be done in house in many vet practices. It will test for adult fluke present in the group and so can diagnose a fluke burden from 10 weeks post infection. The need for there to be mature egg producing fluke to be present in the animal does mean that this test can potentially miss early acute fluke in the autumn where there is a particularly high larval burden as liver damage has occurred before the fluke are mature enough to produce eggs.    

Faecal corpoantigen is a lab test done on dung sample at labs to identify digestive enzymes produced by fluke passed out in the dung of the animal. Due to not requiring egg-producing adult fluke this test can pick up fluke infections up 2-3 weeks sooner than sedimentation and so will give an earlier indication of acute fluke infection. The corpoantigen test is also useful in performing drench checks as it gives the level of fluke infection so a degree of fluke resistance to drench can be determined.  

Fluke ELISA is another lab-based test, it is however done on blood and looks for antibodies produced by the animal against fluke. This test can pick up fluke infection earliest at 2 weeks, but it only proves that the animals have been exposed to fluke and not if they have an active infection. So a positive result may be from fluke exposure in previous years. The best way to apply this test is to use young animals in their first grazing season as sentinel animals, if they have a positive result it can be assumed that there is a fluke exposure in the current grazing season as they have no previous challenge.

Post-mortem can show chronic livers that have had previous fluke infestations, or “impression smears” can be taken of the cut surface of liver to pick up earlier infections. However well-planned management and intervention should help to prevent this being the main method of diagnosing a fluke issue.  

Kill sheets from abattoirs can be an inexpensive method of monitoring how young stock in particular are affected by fluke. Most reports will differentiate between acute and chronic infections and, whilst the time has obviously passed that the individuals can be treated, it will give a good indication of fluke levels on the farm and can help in management strategies for the following year.  

Using the information gathered by these techniques to get a good picture of the fluke dynamics on an individual farm can help farmers plan the appropriate treatment at the appropriate time to help avoid unnecessary losses and treatments.

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iMAGE CREDIT:  NADIS -  Emily Simcock BSc(hons) BVSc(hons) MRCVS PGcert (Ruminant Nutrition) 

For more information.  : https://www.nadis.org.uk/disease-a-z/sheep/liver-fluke-control-in-sheep/